This only applies to Attribute Articulations (which are attached to a specific note & and will move with the note) but not for Direction Articulations (which tell Cubase to use that articulation until you tell it to use something different and are not attached to a note).
To get rid of an Attribute do exactly what you did to initially assign it to the note. It works like a toggle.
To get rid of a Direction select it in Lane at the bottom of the Key Ed and hit delete.
The fact that there are two different flavors of articulations and they don’t work the same can really cause confusion.